[Show abstract][Hide abstract] ABSTRACT: Cytotoxic therapeutic monoclonal antibodies (mAbs) often mediate target cell-killing by eliciting immune effector functions via Fc region interactions with cellular and humoral components of the immune system. Key functions include antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). However, there has been increased appreciation that along with cell-killing functions, the induction of antibody-dependent cytokine release (ADCR) can also influence disease microenvironments and therapeutic outcomes. Historically, most Fc engineering approaches have been aimed toward modulating ADCC, ADCP, or CDC. In the present study, we describe an Fc engineering approach that, while not resulting in impaired ADCC or ADCP, profoundly affects ADCR. As such, when peripheral blood mononuclear cells are used as effector cells against mAb-opsonized tumor cells, the described mAb variants elicit a similar profile and quantity of cytokines as IgG1. In contrast, although the variants elicit similar levels of tumor cell-killing as IgG1 with macrophage effector cells, the variants do not elicit macrophage-mediated ADCR against mAb-opsonized tumor cells. This study demonstrates that Fc engineering approaches can be employed to uncouple macrophage-mediated phagocytic and subsequent cell-killing functions from cytokine release.
[Show abstract][Hide abstract] ABSTRACT: Trastuzumab has been used for the treatment of HER2-overexpressing breast cancer for more than a decade, but the mechanisms of action for the therapy are still being actively investigated. Ab-dependent cell-mediated cytotoxicity mediated by NK cells is well recognized as one of the key mechanisms of action for trastuzumab, but trastuzumab-mediated Ab-dependent cellular phagocytosis (ADCP) has not been established. In this study, we demonstrate that macrophages, by way of phagocytic engulfment, can mediate ADCP and cancer cell killing in the presence of trastuzumab. Increased infiltration of macrophages in the tumor tissue was associated with enhanced efficacy of trastuzumab whereas depletion of macrophages resulted in reduced antitumor efficacy in mouse xenograft tumor models. Among the four mouse FcγRs, FcγRIV exhibits the strongest binding affinity to trastuzumab. Knockdown of FcγRIV in mouse macrophages reduced cancer cell killing and ADCP activity triggered by trastuzumab. Consistently, an upregulation of FcγRIV expression by IFN-γ triggered an increased ADCP activity by trastuzumab. In an analogous fashion, IFN-γ priming of human macrophages increased the expression of FcγRIII, the ortholog of murine FcγRIV, and increased trastuzumab-mediated cancer cell killing. Thus, in two independent systems, the results indicated that activation of macrophages in combination with trastuzumab can serve as a therapeutic strategy for treating high HER2 breast cancer by boosting ADCP killing of cancer cells.
The Journal of Immunology 05/2015; 194(9):4379-4386. DOI:10.4049/jimmunol.1402891 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report a chimeric monoclonal antibody (mAb) directed to a neo-epitope that is exposed in the IgG lower hinge following proteolytic cleavage. The mAb, designated 2095-2, displays specificity for IdeS-generated F(ab') 2 fragments, but not for full-length IgG or for closely-related F(ab') 2 fragments generated with other proteases. A critical component of the specificity is provided by the C-terminal amino acid of the epitope corresponding to gly-236 in the IgG1 (also IgG4) hinge. By its ability to bind to IdeS-cleaved anti-CD20 mAb, mAb 2095-2 fully restored antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against WIL2-S cells to the otherwise inactive anti-CD20 IgG1 F(ab') 2 fragment. Similarly, 2095-2 reinstated ADCC against MDA-MB-231 cells to an anti-CD142 IgG1 F(ab') 2 fragment. mAb 2095-2 was also capable of eliciting both CDC and ADCC to IgG4 F(ab') 2 fragments, an IgG subclass that has weaker ADCC and CDC when intact relative to intact IgG1. The in vitro cell-based efficacy of 2095-2 was extended to the in vivo setting using platelets as a cell clearance surrogate. In a canine model, the co-administration of 2095-2 together with IdeS-generated, platelet-targeting anti-CD41/61 F(ab') 2 fragment not only restored platelet clearance, but did so at a rate and extent of clearance that exceeded that of intact anti-CD41/61 IgG at comparable concentrations. To further explore this unexpected amplification effect, we conducted a rat study in which 2095-2 was administered at a series of doses in combination with a fixed dose of anti-CD41/61 F(ab') 2 fragments. Again, the combination, at ratios as low as 1:10 (w/w) 2095-2 to F(ab') 2, proved more effective than the anti-CD41/61 IgG1 alone. These findings suggest a novel mechanism for enhancing antibody-mediated cell-killing effector functions with potential applications in pathologic settings such as tumors and acute infections where protease activity is abundant.
[Show abstract][Hide abstract] ABSTRACT: The annual European Antibody Congress (EAC) has traditionally been the key event for updates on critical scientific advances in the antibody field, and 2013 was no exception. Organized by Terrapinn, the well-attended meeting featured presentations on considerations for developing antibodies and antibody-like therapeutics, with separate tracks for antibody-drug conjugates, naked antibodies, and multispecific antibodies or protein scaffolds. The overall focus of the EAC was current approaches to enhance the functionality of therapeutic antibodies or other targeted proteins, with the ultimate goal being improvement of the safety and efficacy of the molecules as treatments for cancer, immune-mediated disorders and other diseases. Roundtable discussion sessions gave participants opportunities to engage in group discussions with industry leaders from companies such as Genmab, Glenmark Pharmaceuticals, MedImmune, Merrimack Pharmaceuticals, and Pierre Fabre. As the 2013 EAC was co-located with the World Biosimilar Congress, participants also received an update on European Medicines Agency guidelines and thoughts on the future direction and development of biosimilar antibodies in the European Union.
[Show abstract][Hide abstract] ABSTRACT: Molecularly engineered antibodies with fit-for-purpose properties will differentiate next generation antibody therapeutics from traditional IgG1 scaffolds. A necessary step to engineer the most appropriate properties for a particular therapeutic area requires an understanding of the intricacies of the target microenvironment in which the antibody is expected to function. Our group and others have demonstrated that proteases secreted by invasive tumors and pathological microorganisms are capable of cleaving human IgG1, the most commonly-adopted isotype among monoclonal antibody therapeutics. Specific cleavage in the lower hinge of IgG1 results in a loss of Fc-mediated cell-killing functions without a concomitant loss of antigen-binding capability or circulating antibody half-life. Proteolytic cleavage in the hinge region by tumor-associated or microbial proteases is postulated as a means of evading host immune responses, and antibodies engineered with potent cell-killing functions that are also resistant to hinge proteolysis are of interest. Mutation of the lower hinge region of an IgG1 resulted in protease-resistance, but also resulted in a profound loss of Fc-mediated cell-killing functions. In the present study, we demonstrate that specific mutations of the CH2 domain in conjunction with lower hinge mutations can restore and sometimes enhance cell-killing functions, while still retaining protease-resistance. By identifying mutations that can restore either complement or FcγR-mediated functions on a protease-resistant scaffold, we were able to generate a novel protease-resistant platform with selective cell-killing functionality.
[Show abstract][Hide abstract] ABSTRACT: The Fc variant of IgG2, designated as IgG2, was engineered with V234A/G237A /P238S/H268A/V309L/A330S/P331S substitutions to eliminate affinity for Fcγ receptors and C1q complement protein and consequently, immune effector functions. IgG2σ was compared to other previously well-characterized Fc 'muted' variants, including aglycosylated IgG1, IgG2m4 (H268Q/V309L/A330S/P331S, changes from IgG4), and IgG4 ProAlaAla (S228P/L234A/L235A) in its capacity to bind FcγRs and activate various immune-stimulatory responses. In contrast to the previously characterized silenced Fc variants, which retain selective FcγR binding and effector functions, IgG2σ shows no detectable binding to the Fcγ receptors in affinity and avidity measurements, nor any detectable antibody-dependent cytotoxicity, phagocytosis, complement activity, or Fc-mediated cytokine release. Moreover, IgG2σ shows minimal immunogenic potential by T-cell epitope analysis. The circulating half-life of IgG2σ in monkeys is extended relative to IgG1 and IgG2, in spite of similar in vitro binding to recombinant FcRn. The three-dimensional structure of the Fc, needed for assessing the basis for the absence of effector function, was compared with that of IgG2 revealing a number of conformational differences near the hinge region of the CH2 domain that result from the amino acid substitutions. Modeling reveals that at least one of the key interactions with FcγRs is disrupted by a conformational change that reorients P329 to a position that prevents it from interacting with conserved W90 and W113 residues of the FcγRs. Inspection of the structure also indicated significant changes to the conformation of D270 and P329 in the CH2 domain that could negatively impact C1q binding. Thus, structural perturbations of the Fc provide a rationale for the loss of function. In toto, these properties of IgG2σ suggest it is a superior alternative to previously described IgG variants of minimal effector function, for future therapeutic applications of non-immunostimulatory mAb and Fc-fusion platforms.
[Show abstract][Hide abstract] ABSTRACT: Tumor-associated macrophages (TAMs) have been shown to promote tumor progression, and increased TAM infiltration often correlates with poor prognosis. However, questions remain regarding the phenotype of macrophages within the tumor and their role in mAb-dependent cytotoxicity. This study demonstrates that whereas TAMs have protumor properties, they maintain Fc-dependent anti-tumor function. CD11b(+)CD14(+) TAMs isolated from primary human breast tumors expressed activating FcγRs. To model breast cancer TAMs in vitro, conditioned medium from breast cancer cells was used to drive human peripheral monocyte differentiation into macrophages. Tumor-conditioned macrophages were compared with in vitro derived M1 and M2a macrophages and were found to promote tumor cell invasion and express M2a markers, confirming their protumor potential. However, unlike M2a macrophages, tumor-conditioned macrophages expressed FcγRs and phagocytosed tumor cells in the presence of a tumor Ag-targeting mAb, unmasking an underappreciated tumoricidal capacity of TAMs. In vivo macrophage depletion reduced the efficacy of anti-CD142 against MDA-MB-231 xenograft growth and metastasis in SCID/beige mice, implicating a critical role for macrophages in Fc-dependent cell killing. M-CSF was identified in tumor-conditioned media and shown to be capable of differentiating macrophages with both pro- and anti-tumor properties. These results highlight the plasticity of TAMs, which are capable of promoting tumor progression and invasion while still retaining tumoricidal function in the presence of tumor-targeting mAbs.
The Journal of Immunology 10/2012; 189(11). DOI:10.4049/jimmunol.1201889 · 4.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Introduction
Recent studies reported that human IgG antibodies are susceptible to specific proteolytic cleavage in their lower hinge region, and the hinge cleavage results in a loss of Fc-mediated effector functions. Trastuzumab is a humanized IgG1 therapeutic monoclonal antibody for the treatment of HER2-overexpressing breast cancers, and its mechanisms of action consist of inhibition of HER2 signaling and Fc-mediated antibody-dependent cellular cytotoxicity (ADCC). The objective of this study is to investigate the potential effect of proteinase hinge cleavage on the efficacy of trastuzumab using both a breast cancer cell culture method and an in vivo mouse xenograft tumor model.
Trastuzumab antibody was incubated with a panel of human matrix metalloproteinases, and proteolytic cleavage in the lower hinge region was detected using both western blotting and mass spectrometry. Single hinge cleaved trastuzumab (scIgG-T) was purified and evaluated for its ability to mediate ADCC and inhibition of breast cancer cell proliferation in vitro as well as anti-tumor efficacy in the mouse xenograft tumor model. Infiltrated immune cells were detected in tumor tissues by immunohistochemistry.
scIgG-T retains HER2 antigen binding activity and inhibits HER2-mediated downstream signaling and cell proliferation in vitro when compared with the intact trastuzumab. However, scIgG-T lost Fc-mediated ADCC activity in vitro, and had significantly reduced anti-tumor efficacy in a mouse xenograft tumor model. Immunohistochemistry showed reduced immune cell infiltration in tumor tissues treated with scIgG-T when compared with those treated with the intact trastuzumab, which is consistent with the decreased ADCC mediated by scIgG-T in vitro.
Trastuzumab can be cleaved by matrix metalloproteinases within the lower hinge. scIgG-T exhibited a significantly reduced anti-tumor efficacy in vivo due to the weakened immune effector function such as ADCC. The results suggest that the lower hinge cleavage of trastuzumab can occur in the tumor microenvironment where matrix metalloproteinases often have high levels of expression and scIgG-T might compromise its anti-tumor efficacy in the clinic. However, further studies are needed to validate these hypotheses in the clinical setting.
Breast cancer research: BCR 08/2012; 14(4):R116. DOI:10.1186/bcr3240 · 5.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Immunoglobulin G (IgG) antibodies are an integral part of the adaptive immune response that provide a direct link between humoral and cellular components of the immune system. Insights into relationships between the structure and function of human IgGs have prompted molecular engineering efforts to enhance or eliminate specific properties, such as Fc-mediated immune effector functions. Human IgGs have an N-glycosylation site at Asn297, located in the second heavy chain constant region (CH2). The composition of the Fc glycan can have substantial impacts on Fc gamma receptor(FcγR) binding. The removal of the glycan through enzymatic deglycosylation or mutagenesis of the N-linked glycosylation site has been reported to "silence" FcγR-binding and effector functions, particularly with assays that measure monomeric binding. However, interactions between IgGs and FcγRs are not limited to monomeric interactions but can be influenced by avidity, which takes into account the sum of multimeric interactions between antigen-engaged IgGs and FcγRs. We show here that under in vitro conditions, which allowed avidity binding, aglycosylated IgGs can bind to one of the FcγRs, FcγRI, and mediate effector functions. These studies highlight how the valency of a molecular interaction (monomeric binding versus avidity binding) can influence antibody/FcγR interactions such that avidity effects can translate very low intrinsic affinities into significant functional outcomes.
[Show abstract][Hide abstract] ABSTRACT: The evolution of therapeutic antibodies has encompassed multiple engineering efforts in the hope of improving the efficacy, safety, and duration of effects of antibody-based drugs. Advances in protein engineering technologies afforded investigators the ability to overcome problems associated with introducing foreign antibodies into humans. These efforts included antibody chimerization, humanization, and the more recent development of human antibodies, all of which reduced anti-drug immune responses. Additional efforts have engineered antibody variable regions that encode multiple specificities into a single molecular entity. Apart from optimizing antigen-binding capabilities and reducing immunogenicity, many advances have been made that modulate an antibody’s ability to interact with cells and serum components of the immune system. Manipulation of antibody glycosylation or the amino acid sequence has had a significant impact on recruitment of the Fc-dependent effector functions. This chapter presents an overview of V region and Fc modifications and focuses on advances in engineering to tailor an antibody’s function relative to the intended therapeutic need.
Development of Antibody-Based Therapeutics, 01/2012: pages 65-93; , ISBN: 978-1-4419-5953-9
[Show abstract][Hide abstract] ABSTRACT: The mammalian antibody repertoire comprises immunoglobulin (Ig) molecules of multiple isotypes and subclasses with varying functional properties. Among the four subclasses of the human IgG isotype, we found that IgG2 exhibits a particular resistance to human and bacterial proteases that readily cleave the IgG1 hinge region in vitro. Autoantibodies (IgGs) that recognize points of proteolytic cleavage in the IgG1 hinge are widespread in the healthy human population, suggesting that IgG1 fragmentation and the generation of cryptic antigens for host immune surveillance commonly occur in vivo. We previously reported that autoantibodies to cleaved IgG1s can restore Fc-mediated effector functions that are lost following proteolytic cleavage of the hinge. In contrast, it was not possible to demonstrate an analogous cohort of autoantibodies to IgG2 hinge epitope analogs, and there appeared to be no functional component in human serum with the ability to reconstitute Fc effector functions to a cell-bound IgG2 fragment. Thus, the results indicate that among the IgG subclasses, human IgG2 is uniquely resistant to a number of known pathological proteases and that autoimmune recognition to potential cleavage points in the IgG2 hinge appears to be absent in human circulation.
[Show abstract][Hide abstract] ABSTRACT: Human anti-IgG hinge (HAH) autoantibodies constitute a class of immunoglobulins that recognize cryptic epitopes in the hinge region of antibodies exposed after proteolytic cleavage, but do not bind to the intact IgG counterpart. Detailed molecular characterizations of HAH autoantibodies suggest that they are, in some cases, distinct from natural autoantibodies that arise independent of antigenic challenge. Multiple studies have attempted to define the specificity of HAH autoantibodies, which were originally detected as binding to fragments possessing C-terminal amino acid residues exposed in either the upper or lower hinge regions of IgGs. Numerous investigators have provided information on the isotype profiles of the HAH autoantibodies, as well as correlations among protease cleavage patterns and HAH autoantibody reactivity. Several biological functions have been attributed to HAH autoantibodies, ranging from house-cleaning functions to an immunosuppressive role to restoring function to cleaved IgGs. In this review, we discuss both the historic and current literature regarding HAH autoantibodies in terms of their origins, specificity, and proposed biological relevance.
The Scientific World Journal 05/2011; 11:1153-67. DOI:10.1100/tsw.2011.107 · 1.73 Impact Factor